Allow to use EitherOrBoth<T> to mean the same as EitherOrBoth<T, T>

src/either_or_both.rs

@@ -6,7 +6,7 @@ use either::Either;
 
 /// Value that either holds a single A or B, or both.
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
-pub enum EitherOrBoth<A, B> {
+pub enum EitherOrBoth<A, B = A> {
     /// Both values are present.
     Both(A, B),
     /// Only the left value of type `A` is present.